As Rivrguy noted, putting those carcasses out is very labor intensive. Plus, of course, you need access to the stream(s). The disease protocols are a major constraint.

The other piece is that all the carcasses that come back to all the hatcheries are (maybe) enough for one river system. We are in that big of a hole.

Further, our Legislature has mandated where some of the fish go; there are all sorts of rules about what can be done with them.